Many household electrical appliance can be hazardous if not properly used and monitored. There are many recorded instances of disastrous home fires caused by unauthorized operation of a household appliance such as a stove by children, burglars or vandals, or persons of reduced capacity or faculties such as the elderly. It is thus advantageous to be able to selectively control the use of such appliances.
In the prior art, means have been provided to prevent unauthorized usage of electrical appliances, primarily through key operated electro-mechanical circuit interrupt devices. However, such devices conventionally provide for on-off control only, meaning that the device completely interrupts the flow of electrical power to the appliance while the interrupt or "locked" state, and it connects the appliance to the electrical supply in the operative or "unlocked" state. In the case of, for example, a stove, once the supply power has been cut off auxiliary electrical equipment such as lighting and an electrical clock also ceases to function.
The present invention provides a security power interrupt for an electrical appliance whereby the appliance retains a connection to the power supply while in interrupt or "locked" mode; complete power shutoff only occurs when a preset electrical current is exceeded, thus allowing operation of the appliance's auxiliary electrical equipment while the device is in the interrupt mode.
In a preferred embodiment, the security power interrupt device of the present invention is controlled by a detachable electronic keypad, whereby a predetermined sequence of key strokes interrupts or restores power to the appliance. Power is supplied to the keypad by a DC current transformed from the wall outlet into which the device is plugged, and the appliance is in turn plugged into the main body of the device. Also in the preferred embodiment, the keypad is connected by a wire remotely from the main body of the device, allowing flexibility in the placement of the keypad. For this purpose the keypad may be provided with a magnet, for detachably affixing the keypad to the metallic housing of the appliance.
Further, the keypad is detachable from the device, thus preventing the interrupt device from being switched out of the interrupt mode and thereby preventing attempts to break the coded key sequence and restore normal supply power to the appliance. The device automatically switches to the interrupt mode when the correct numerical sequence is entered on the keypad, when the keypad is disconnected from the device or after a preset time interval has passed since the last authorized use of the appliance.